10 Gold KeysSo far, Lucy has obtained 10 Gold Keys and 5 Silver Keys, a considerable amount of Keys for a single Celestial Spirit Mage. Lucy's ability to summon her Spirits is limited by how much Magic Power she has to sustain them, the more Spirits she summons and the more powerful they are, the more Magic Power she exhausts.
As of right now, Lucy has 9 of the golden (zodiac) keys. 10 if she had not sacrificed Aqaurius to summon the Celestial Spirit King into battle. But the Aquarius key was reborn (along with Aquarius herself) - Lucy just has to find her. Lucy also has uhm 4 or 5 silver keys (plue, the clock dude, etc.).
No there is not any limits from him anymore.
Nothing. He would never hit himself with his full power, so it'd be like if you accidentally pulled your hands back and hit yourself.
"Sakura's Feelings" (サクラの想い, Sakura no Omoi) is episode 206 of the Naruto: Shippūden anime.